ZA50

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The ZA50, or simply ZA, is the automatic, two speedengine found on some Puch mopeds. It can be distinguished from the one speed Puch engine by the more rectangular shape of the right side engine/transmission cover.

Variations

There were several variations of the ZA50 made. Most notably an oil-injected version and a non-oil-injected version. Additionally, a 2hp/1.5hp version was produced along with a 1hp version. The 2hp and 1.5hp versions have the same internal gearing and are differentiated by the stock top end, whereas the 1hp has different internal gearing. You can identify which version you are working with by counting the teeth on the internal gears:

Clutch Drum

1 hp = 13T

1.5 or 2 hp = 16T

1st Speed Gear

1hp = 73T

1.5 or 2 hp =70T

2nd Speed Gear / Main Shaft

1 hp = 66/14T

1.5 or 2 hp = 64/14T

2nd Speed Driving Plate

1 hp = 20T

1.5 or 2 hp = 22T

Rebuilding

Aftermarket bearings and seals are available for the ZA50. Some say that certain aftermarket bearings aren't exactly the same as the stock bearings, which cause problems with crank shimming and binding. Others have used aftermarket bearings with no troubles. It is important that you take accurate measurements to be sure everything is right. Also, take note of the different ZA50 variations and be sure that you get the correct bearings for whatever version you have.

Weak Points

There are a lot of weak points to the ZA50 motors, if they are built correctly, they can live long and fulfilling lives. Here is a list of the weak points of the motors and how to fix them (if possible).

Pucks

The shock of the motor shifting between first and second is not enough to sheer the teeth of the gears unless the shift dampeners are cranked or no longer exist inside the 2nd gear drive shaft. The stock pucks have been inside the motor for over 20 years; if the bike sat for any amount of time without being run or without trans fluid, at least one if not all the pucks dried out. When they are used again they are quickly shredded. Even perfect pucks can be destroyed in minuets with an 80 Metra installed on a ZA50. When the pucks go, there is nothing to absorb the impact of the shift between 1st and 2nd gear. What takes the brunt of this is the hardened teeth of the 2nd gear main shaft, the starter plate teeth or the gear that is meshed to the 2nd gear main shaft. Since they are hardened, the teeth are quite brittle and once one or two teeth go, slop is created and more teeth quickly follow.

Fix- There are multiple people selling replacement pucks these days. I make my own and have not seen a broken tooth on any motor I have rebuilt with them.

Crank

Just like running a one speed stock crank on a kitted bike, they fail. The only two failures I have seen on a motor I built were my Metra that has a small end bushing failure and my friend J’s bike that had a big end bearing failure.

Fix – Easy: Get a roller con-rod and have it pressed into the stock crank. The cost of the rod + the labor gets you in around $100.

Shims

Lots of places to mess stuff up. There is no easy way to measure the proper end float (possibly there is, check out "better fix" below). If you pull the motor apart to replace the crank bearings you are going to need to re-spec the crank shims. This is a pain in the ass with or without the factory tool or puller. It’s a lot of trial and error with trying to get the clearance tight enough so there is minimal crank slop, but not too tight to the point where the crank binds when you tighten the case bolts down. Unless you have spare shims (they range from .001” – .012”) this can be even harder to get right. Then there are the trans cover shims that are super easy to set if you have the tool but a pain if you don’t. Too tight and you could spin a bearing in the case or blow a hole the size of the bearing in your trans cover.

Fix – Get the tools, hire someone that does, spend your time and figure another way to measure the correct spec.

Better Fix - Forget about calipers, straight edges and factory tools. Use something compressible to measure your end float. Plasti-gauge is a measuring tool that can be used without calipers. No special tools required, perfect for those who don't have calipers and want to build a ZA. Simply place between two shims, tighten clutch cover down, remove clutch cover, separate shims and measure. Adjust shims, verify again and reassemble. Available at most any autoparts store. Check it out here

Clutches

These are not so much an issue with mild or even higher powered motors, after 500+ miles my Metra clutches looked new. But the Parma set-up is quite hard on clutches so I figured I would touch on the subject. My Parma has shredded 1 1st speed clutch and is probably most of the way through its replacement. The linings have a tendency not to wear evenly and tend to chip and erode at the leading edge. I think this has a lot to do with the old glue slowly letting go. I have a few clutches that linings came off as one complete piece. The other issue is the pads use links of chain to pivot. These pieces of chain bend and flex over time and it causes the clutches to kind of bowl inward. This causes there to be less surface area of the clutch to engage the bell so the area that is engaging wears that much faster.

Fix – Since this is not such a big issue with most motors I have not really experimented with fixes yet. I have been talking to a few epoxy distributors and a few companies that make flexible kevlar break/clutch lining material as a replacement to the stock friction material.

Performance Modifications

There are not many things you can do inside an ZA50 to improve performance. The one big thing you have to work with is the clutches.

2nd speed clutch flip

Disassemble your transmission until you get to your clutches. Flip the 2nd speed clutch over so the springs on both clutches face the transmission cover. This changes how the clutch arms rotate in relation to the outward force pulling them toward the clutch bell. They resist the pull until a higher rpm. This can delay the shift point into second gear approximately 5-10mph.

Change oil weight

Using fluid other than the recommended Type-F (most run 10w30 gear oil) will change when both 1st & 2nd gears engage. I'm assuming that this has to do with the thicker oil causing more RPMs (force) to pull the clutch arms into contact with the clutch bell. In addition the higher viscosity oil coats the internal parts better making sure the bearings stay lubricated. Please also overfill your transmission by 50% (stock calls for 9oz I run around 12-15oz). The bearing in the transmission cover are splash lubed meaning the oil level in the motor dose not reach them but the splashing from all the gear teeth keep them running smooth. DO NOT FILL the trans with too much fluid, it will cause too much crankcase pressure and could cause your seals to leak.

Remove Weight from clutches

Just like on a one speed the two speed clutches are centrifugal. Lighter weight clutch arms will require a higher rpm to be pulled out. You can go too far with this, If you remove too much weight from 1st gear it could never grab, If you remove too much from the 2nd clutch it might never shift into 2nd gear. Small amounts or weight removal & trial and error are key. To safely remove material with out damaging the springs you should disassemble them.

Cutting the clutch spring

Making the clutch spring shorter will increase the tension on the clutch arms preventing them from moving out until a higher RPM is reached.

External Gearing

ZA50 internal gearing is different than E50 internal gearing and must be compensated for with different external gearing. Reference this page for a gearing calculator: Puch ZA50 RPM and speed chart